The effects of grevillea robusta trees on some soil chemical and physical propertis in semi arid areas: "a case study of Katheka-kai and Katelembu locations of Mumbu Division , Machakos district, Kenya"
Nthenge, Fidelis N.
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This study was an "Analysis of the fertility of soils under Grevillea robusta trees in the Katheka-Kai and Katelembu locations of Mumbuni Division, Machakos District, Kenya". On - farm research was undertaken in the settlements at Katheka-Kai and Katelembu, with Alisols and Luvisols respectively. Exotic Grevillea robusta trees had been planted in these farms. Soil samples were collected from the plough layer, using soil auger and core rings. These undisturbed samples were collected from four equidistant points in between rows of Grevillea robusta trees,in four replicates. The samples of about 500g - 1000g were put in polythene sample bags, later dried, ground and sieved through 2mm sieve for laboratory analysis. In the laboratory, they were analysed for pH, Organic Carbon, Nitrogen, Phosphorus, Exchangeable bases and Texture. The physical and chemical soil properties obtained were discussed with respect to the effect of Grevillea robusta, by considering distance from the rows of Grevillea robusta, depth of the soil samples and differences between the Alisols and Luvisols. Coefficient correlations were later calculated to determine the relationship between the different soil fertility parameters. A Multiple Stepwise linear regression model was used to study the interrelationships. The high levels of correlation between various soil fertility parameters was mainly attributed to the Grevillea robusta trees, because of the addition of organic matter into the soil via litter decay. This supports the general hypothesis that agroforestry systems would improve the soil as a habitat for plants. Finally, recommendations were given for greater adoption of these tree crops into the modem farming systems.